Self-supporting transducer assembly

ABSTRACT

A self-supporting transducer assembly, mounted, for example, on the nose section shell of a torpedo, comprising an attachment ring; a diaphragm consisting of: (1) a tension-carrying skin, sealably connected to the inner periphery of the attachment ring, and forming with it a dish-shaped cavity; (2) an acoustically non-refractive and non-reflective composite material in the dishshaped cavity; (3) a vapor seal, sealably connected to the inner periphery of the attachment ring, serving, with the tensioncarrying skin, to confine the composite material to the dishshaped cavity; an acoustic isolation joint, mounted on the torpedo, for acoustically isolating the transducer assembly from the torpedo; and at least one transducer element bonded directly to the tension-carrying skin.

United States Patent 151 3,663,934 Whitehouse et al. 1 May 16, 1972 54 TRANSDUCER 3,489,994 1/1970 Massa ..340/1o x [72] Inventors: Harps John Whitehouse, Hacienda Heights; Shelby F. Sullivan, Arcadia, both of Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy [22] Filed: Oct. 8, 1969 [21] Appl. No.2 864,814

3,409,869 11/1968 McCool et al. ..340/8 MM Primary Examiner-Benjamin A. Borchelt Assistant Examiner-H. A. Birmiel Attorney-Richard S. Sciascia, Ervin F. Johnston and John Stan [57] ABSTRACT A self-supporting transducer assembly, mounted, for example, on the nose section shell of a torpedo, comprising an attachment ring; a diaphragm consisting of: l a tension-carrying skin, sealably connected to the inner periphery of the at- [52] U.S. Cl. ..340/9, 340/8 MM, 3310.013 tachmem ring and forming with it a dish shaped cavity; (2) an [51] Int Cl "04b 11/00 acoustically non-refractive and non-reflective composite 58 Field of Search ..340/& RT, 8 MM, 9, 14 material in l f (3) a sealably connected to the inner periphery of the attachment ring, serv- ISM References Cited ing, with the tension-carrying skin, to confine the composite material to the dish-shaped cavity; an acoustic isolation omt, UNITED STATES PA'I-ENTS mounted on the torpedo, for acoustically isolating the transducer assembly from the torpedo; and at least one transducer 33nd, t element bonded directly to the tension-carrying skin. assa, r." 3,466,017 9/l969 Malvin ..340/l4 X 7 Claims, 2 Drawing Figures 40 2o 48 46 I 24 i 32 w l8 44 52 42 26 I4 54 64 S i {\w a K 28 e2 58 2 5 3O 5O 6O 0 5' l2 3 4 l6 i/ Patented May 16, 1972 .E N l SS O 0326 .0 22M RU T 00 S 6 TH N 4 l NE H 6 4 6 O uvw 4 5 N U 2 lwLF O NU 2 5 8 l. .V H 5 5m x m mWFR m x F E d RY EBY. 8 PL 4 M RE 4 2 AH 5 6 HS 4 w G 4 6 4 8 F 4 O l 2 3 B 4 7 O 2 ATTORNEY.

JOHN STAN, AGENT.

SELF-SUPPORTING TRANSDUCER ASSEMBLY The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a self-supporting transducer assembly located on the nose cone of a torpedo.

In the field of support assemblies for transducers located on the nose cone of a torpedo and used for detecting and tracking a target, it has been the general practice to back the transducer heads with what is termed a pressure release paper and a pressure backup plate so that the pressure transmitted by a non-self-supporting rubber diaphragm is ultimately transmitted to the somewhat rigid pressure backup plate. The difficulty with this method is that the pressure release paper changes characteristics with increasing pressure and becomes nonfunctional at pressures less than the design depth of the transducer. Any time that a fairly substantial structure has to be put behind the transducer element to hold it, that is to keep it from collapsing, then unavoidably energy is coupled to that structure. This complicates the transducer design because if the backup structure varies as the paper varies, the acoustic tuning changes. The self-supporting structure of this invention is much simpler and has a more efficient transducer design.

In the invention herein described, the face of the transducer element is coupled to the ocean through a diaphragm consisting of a tension-carrying skin, a composite matrix, and a vapor sea], usually another thin skin. The diaphragm is so designed that it has the same acoustic impedance as the seawater. Therefore, as far as the transducer elements are concerned they are looking directly into the ocean.

Accordingly, an object of the present invention is the provision of a self-supporting transducer assembly wherein the transducer heads are not restrained by pressure-sensitive backing paper.

Another object is to provide a self-supporting transducer assembly wherein the acoustic and electrical performance is essentially independent of pressure up to the design strength of the composite diaphragm.

A further object of the invention is the provision of a selfsupporting transducer assembly including a diaphragm of composite material, with transducer elements attached thereto, which do not have additional, rigid material constraining their heads.

Other objects and many of attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description, when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a cross-sectional view through the nose cone of a torpedo, showing a preferred embodiment of the self-supporting transducer assembly.

FIG. 2 is a similar type of view showing another embodiment of the self-supporting transducer assembly.

Referring now to the drawings, wherein like reference nu merals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a self-supporting transducer assembly 10, mounted, for example, on the nose section shell of a torpedo, including a support 12, having the form of a shell with an opening in the middle, and could form an integral part of the nose section shell itself. The nose section shell is sometimes called the transducer shell. Its specific function herein is that of a support for the transducer assembly 10. The support 12 has a plurality of clearance holes 14 aligned in the direction of the axis of the torpedo 16, and an O-ring groove 18, encircling all of the clearance holes. An acoustic isolation joint, mounted on the support 12 acoustically isolates the support from the other parts of the transducer assembly 10, and serves to acoustically isolate the transducer assembly from shell-home noise. An attachment ring 20, surrounding the opening in the support 12, is sealably connected to the support by the acoustic isolation joint. The attachment ring has a plurality of slots 22 with parallel sides which are perpendicular to the axis 16 of the torpedo and a plurality of tapped holes 24 which are aligned with the clearance holes 14 of the support 12.

Discussing now in more detail the acoustic isolation joint, an essential element is an O-ring 26 mounted in the groove 18 in the support 12. A plurality of bolts 28, one for each hole 14, draw the attachment ring 20 to the support 12, and pass through a pair of acoustic isolating washers, a lower washer 30 being located between the head of the bolt 28 and the support 12, the upper washer 32 being slipped into the slot 22 for each bolt. Lower and upper acoustic isolating washers 30 and 32 may be made of the material called Min-K 2000, manufactured by the Johns-Manville Company of New York, NY. This material has a very low acoustic impedance in seawater, lower than that of seawater, and consists essentially of silica particles of sub-micron size in a phenolic binder. A process for making a similar material is fully described in the patent hav-' ing the U.S. Pat. No. 3,542,723 which issued on Nov. 24, 1970 titled Method of Molding Aggregate Pressure Release Material, and assigned to the same assignee as the subject application. The bolts 28, when screwed into the tapped holes 24 compress the two washers 30 and 32 and the O-ring 26, thereby making a watertight seal between the attachment ring 20 and the support 12.

It should be pointed out at this point that the diameter of the attachment ring 20 where the upper, acoustic, isolating, washer 32 is positioned is purposely made very thin so that the part of the attachment ring which is between the upper washer and the support 12 or transducer shell can be flexed to some extent. The wall thickness of the attachment ring 20 at its narrowest point is as thin as possible, so that the acoustic coupling around it is minimized and yet just thick enough to prevent it from rupturing or breaking.

The self-supporting transducer assembly 10 further comprises a diaphragm 40 consisting of a tension-carrying skin 42, sealably connected to the inner periphery 44 of the attachment ring 20, extending across the opening in the support 12 and forming with the attachment ring a dish-shaped cavity.

In a specific embodiment, the tension-carrying skin 42 consisted of a thin sheet of material having a high-strength and high modulus, such as titanium. The thickness of the titanium would be a factor in determining how rigid the diaphragm 40 was. Stainless steel or a sheet made of boron or glass may also be used as a tension-carrying skin 42.

The dish-shaped cavity is filled with an acoustically nonrefractive and non-reflective composite material 46, consisting essentially of a predetermined proportion of glass microspheres, filled with a gas at low pressure, and interspersed in a resin base, such as an epoxy resin. The method of making a composite material 46 which is prestressed to a predetermined pressure is completely described in the patent application having the Ser. No. 811,069, dated Mar. 27, 1969, titled Structural Material with Controlled Gas Entrapment, and assigned to the same assignee as the subject invention.

The relative proportions of the crushed and uncmshed glass and of the base material, consisting for example of an epoxy resin or polyurethane, which comprises the composite matrix 46 will vary to a great extent depending upon the ambient surroundings in which the transducer assembly 10 is to be used.

The material of the diaphragm 40 must meet two rather rigid requirements: (1) it must act as an acoustic window; and (2) it must have enough structural rigidity to avoid collapsing in actual use. The specific proportions required for the material of the diaphragm 40 so that it has the required acoustic properties and the required strength will vary and actually form a family of proportions.

A particularly successful formulation included gm of an epoxy resin known under the trade name of Epon 815, and manufactured by the Shell Chemical Co., a division of the Shell Oil Co. in New York, NY. To this amount was added 10 gm of a hardener known by the trade name of DEAP' (diethylamine propylamine) and manufactured by the same company, and 10.5 gm of glass microspheres, known under the trade name of Glass Bubbles, type B35A, sold by the Reflective Products Division of the 3M Company, in Minneapolis, Minn. In a typical assortment of the microspheres, 90 percent of them will be between 20 and 80 microns in size.

A vapor seal 48, sealably connected to the attachment ring 20 at the outer side of the shell, serves, with the tension-carrying skin 42, to confine the composite material 46 to the dishshaped cavity. The vapor seal 48 may be a thin sheet of metal, for example, aluminum. The vapor seal 48 is needed when the composite matrix 46 is porous and would otherwise absorb the seawater. The characteristics of the composite matrix 46 would change completely if seawater could penetrate it, and this is why a vapor seal 48 may be required. The acoustic density p and the acoustic velocity would change drastically, and therefore the acoustic impedance would change.

When the composite matrix 46 consists of crushed glass in an epoxy resin, it would be a simple matter to put a layer of epoxy on top of the composite matrix and thereby make a vapor seal 48.

If the vapor seal 48 were a strip of metal it would have to be made to adhere in some manner to the composite matrix 46, for example by using an adhesive of some kind, or by evaporating the metal onto the composite matrix.

The final major component of the transducer assembly is the transducer 50. The transducer assembly comprises a twodimensional array of transducers, of which an end view is shown in the figures. They are bonded directly to the inner surface of the tension-carrying skin 42, for example, with an epoxy-based adhesive.

On the other hand, the transducer array when used for transmitting requires a large number N of transducers 50 to form the desired transmission pattern. N independent signal sources are required. Each transducer element 50 is a transmitting and receiving element, and may be considered to be a piston-like transmitter or receiver. As a receiver, each transducer element 50 samples the acoustic sound field at statistically independent points. As transmitters, they are used to form the radiation pattern for the transmitter array.

Discussing now the specific structure of each transducer element 50, the transducer element has an aluminum base 52, a cylindrical ceramic transducer body 54 and a tungsten or steel end 58. Each transducer element 50 has a central hole 60 within which is a conductor or rod 62, for example, of beryllium copper, which is connected to a common ground, the tension-carrying skin 42. An ungrounded lead 64 encircles each transducer element 50. The electrical potential is developed across the ungrounded wire 64 and the rod 62.

In some embodiments, a separate tension-carrying skin 42 was not used, the transducer elements 50in that case being attached directly to the composite material 46. While the diaphragm 40 was in this instance not as rigid as when a metallic tension-carrying skin 42 was present, it did perform satisfactorily. A separate tension-carrying skin 42 would in general be absent only if it were known in advance that the torpedo would be used only at comparatively low depths.

FIG. 2 shows another embodiment of the self-supporting transducer assembly 70 wherein the tension-carrying skin 72 may be of a fibrous material, for example, fiber glass, which is placed in position over one part 74A of a two-part attachment ring 74. The upper part 743 of the attachment ring is then screwed onto the lower part 74A.

In some other embodiment of the self-supporting transducer assembly, not shown, the diaphragm 40 might consist of a homogeneous fibrous material strong enough to not require a tension-carrying skin, nor a vapor seal, the fibrous material itself being impervious to seawater. As an example, the entire diaphragm 40 may consist of a mixture of fiberglas fibers and crushed glass in an epoxy resin base. This composite material has enough mechanical strength to not require a separate tension-carrying skin 42.

The diaphragm 40 consisting of the tension carrying skin 42, the composite matrix 46, and the vapor seal 48 actually comprises an acoustic window and permits acoustic energy to be readily transmitted through it. The components of the diaphragm are so chosen that the resultant combination is nonrefractive and nonreflective.

The design of the self-supporting transducer assembly 10 and involves various compromises or tradeoffs. It is desirable that the torpedo be able to operate at great depths, but this then necessitates a diaphragm 40 which is capable of being subjected to a great stress. This necessitates having a structure having the required strength for supporting the transducer array 10 or 70. On the other hand, a substantial structure interferes with the operation of the diaphragm 40 as an acoustic window. Therefore, a compromise must be effected between these two requirements.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

We claim:

1. A self supporting transducer assembly, which may be used on a torpedo, comprising;

an attachment ring having a central opening;

a diaphragm sealably mounted to the ring across the central opening and made of an acoustically nonrefractive and nonreflective, composite, self-supporting, material which is impervious to seawater;

at least one transducer element directly bonded to the diaphragm for self support thereto;

a support for the ring; and

means acoustically isolating the ring from the support and sealably connecting the ring thereto.

2. A self-supporting transducer assembly according to claim 1, wherein the diaphragm consists of:

a tension-carrying skin, sealably connected across the attachment ring and forming with it a dish-shaped cavity;

an acoustically nonrefractive and nonreflective composite material in the dish-shaped cavity;

a vapor seal, consisting of a thin sheet of material which is impervious to seawater, sealably connected across the attachment ring serving, with the tension-carrying skin, to confine the composite material to the dish-shaped cavity; and wherein the transducer element is bonded to the tension-carrying skin, the axis of the transducer being parallel to the axis of the ring.

3. A self-supporting transducer assembly according to claim 2 wherein the attachment ring has a plurality of slots with parallel sides, the sides being parallel to and below the tensioncarrying skin, the attachment ring having a plurality of tapped holes in a direction parallel to the axis of the ring;

the ring support has a plurality of clearance holes aligned in the direction of each of the tapped holes; and further comprising:

a plurality of resilient washers, a pair for each hole, one washer of each washer pair being located in each slot, the other washer being located at the surface of the diaphragm support;

an O-ring mounted in a groove in the diaphragm support, the groove forming a periphery which encompasses all of the bolt holes; and

a plurality of bolts, one for each hole, each bolt passing through a pair of washers, the bolts when screwed into the tapped holes compressing the two washers and the O- ring, thereby making a watertight seal between the attachment ring and the support.

4. A self-supporting transducer assembly according to claim 3, wherein the composite material consists of a homogeneous mixture of glass microspheres, containing a gas at low pressure, interspersed in an epoxy resin, the composite material being prestressed to a pressure equal to the maximum pressure at which the self-supporting transducer assembly 6. A self-supporting transducer assembly according to claim is to be used. 5 wherein il Self-Supporting transducer assembly according to daim the tension-carrying skin is an elastomeric material. 4 w erein the attachment ring is in two sections, one section capable 5 of being screwed into the other section, and

the tension-carrying skin is placed between the two sections of the attachment ring.

6, wherein the elastomeric material is of fiberglas.

7. A self-supporting transducer assembly according to claim. 

1. A self supporting transducer assembly, which may be used on a torpedo, comprising; an attachment ring having a central opening; a diaphragm sealably mounted to the ring across the central opening and made of an acoustically nonrefractive and nonreflective, composite, self-supporting, material which is impervious to seawater; at least one transducer element directly bonded to the diaphragm for self support thereto; a support for the ring; and means acoustically isolating the ring from the support and sealably connecting the riNg thereto.
 2. A self-supporting transducer assembly according to claim 1, wherein the diaphragm consists of: a tension-carrying skin, sealably connected across the attachment ring and forming with it a dish-shaped cavity; an acoustically nonrefractive and nonreflective composite material in the dish-shaped cavity; a vapor seal, consisting of a thin sheet of material which is impervious to seawater, sealably connected across the attachment ring serving, with the tension-carrying skin, to confine the composite material to the dish-shaped cavity; and wherein the transducer element is bonded to the tension-carrying skin, the axis of the transducer being parallel to the axis of the ring.
 3. A self-supporting transducer assembly according to claim 2 wherein the attachment ring has a plurality of slots with parallel sides, the sides being parallel to and below the tension-carrying skin, the attachment ring having a plurality of tapped holes in a direction parallel to the axis of the ring; the ring support has a plurality of clearance holes aligned in the direction of each of the tapped holes; and further comprising: a plurality of resilient washers, a pair for each hole, one washer of each washer pair being located in each slot, the other washer being located at the surface of the diaphragm support; an O-ring mounted in a groove in the diaphragm support, the groove forming a periphery which encompasses all of the bolt holes; and a plurality of bolts, one for each hole, each bolt passing through a pair of washers, the bolts when screwed into the tapped holes compressing the two washers and the O-ring, thereby making a watertight seal between the attachment ring and the support.
 4. A self-supporting transducer assembly according to claim 3, wherein the composite material consists of a homogeneous mixture of glass microspheres, containing a gas at low pressure, interspersed in an epoxy resin, the composite material being prestressed to a pressure equal to the maximum pressure at which the self-supporting transducer assembly is to be used.
 5. A self-supporting transducer assembly according to claim 4 wherein the attachment ring is in two sections, one section capable of being screwed into the other section, and the tension-carrying skin is placed between the two sections of the attachment ring.
 6. A self-supporting transducer assembly according to claim 5, wherein the tension-carrying skin is an elastomeric material.
 7. A self-supporting transducer assembly according to claim 6, wherein the elastomeric material is of fiberglas. 